Did Dinosaurs Break the Sound Barrier?

By JOHN NOBLE WILFORD

Published: December 2, 1997

MOVE over, Chuck Yeager, and give way to supersonic dinosaurs.

At least 150 million years before Mr. Yeager in 1947 became the first human to break the sound barrier in a rocket plane, the largest dinosaurs, a group known as sauropods, could have mustered the right stuff to send sonic booms resounding over the Mesozoic landscape. No, the 100-ton creatures never got off the ground. All they would have had to do was flick their long tails like a bullwhip.

The idea had occurred to some paleontologists examining fossils of the enormous sauropod tails, which tapered to thin tips. Could they have been used like whips to defend themselves or to produce a loud ''crack'' to intimidate predators or communicate with fellow sauropods, including potential mates? As physicists have known since 1958, the crack of a whip is actually the shock wave, or sonic boom, caused by the thin tip of a whip exceeding the speed of sound for one moment.

No one had put the idea to a test until a master of computer simulations, Dr. Nathan P. Myhrvold of the Microsoft Corporation, struck up an extended electronic-mail conversation with a leading dinosaur expert, Dr. Philip J. Currie of the Royal Tyrrell Museum of Paleontology in Drumheller, Alberta. The result could be the beginning of a new research specialty that Dr. Myhrvold calls cyberpaleontology.

In analyzing fossils and developing computer models of sauropod tails, the two researchers said they had found evidence that dinosaurs like Apatosaurus (also known as Brontosaurus) and Diplodocus could indeed have flicked their tails to supersonic velocities. But the sonic booms produced by the 3,500-pound tails of these behemoths would probably have sounded more like cannon fire than the crack of a bullwhip.

Dr. Myhrvold and Dr. Currie described the research in interviews and in a report in this month's issue of the journal Paleobiology. They conducted a variety of computer simulations, testing different assumptions about the biomechanical capabilities of these giant dinosaurs. They compared tails with whips in their computer analysis to see how similarly they behaved.

''In all cases, it was easy to find simulations that produced supersonic motion,'' the scientists wrote. ''The geometric scaling of vertebral dimensions found in the various diplodocids strongly suggests that any of them, or non-diplodocid sauropods with 'whiplash' tails, would share this capability.''

With one side-to-side flick, the researchers determined, a wave of energy could accelerate through the length of one of the tapering, segmented tails, gaining momentum to propel the tip of the tail to velocities of more than 750 miles an hour, faster than the speed of sound.

''We must confess that it is pleasing to think that the first residents of Earth to exceed the sound barrier were not humans, but rather the diplodocid sauropods,'' Dr. Myhrvold and Dr. Currie concluded.

Other dinosuar experts are sharply divided over the research. Gregory S. Paul, an independent specialist in dinosaur anatomy who is based in Baltimore, said he thought the concept of sauropods with supersonic tails was physically plausible. But at a recent paleontology conference, he said, he heard ''other people who just hate the idea.''

One critic is Dr. Kenneth Carpenter, a paleontologist at the Denver Museum of Natural History. ''To be blunt,'' he said in an interview, ''the computer simulations are another case of garbage in, garbage out.''

Dr. Carpenter questioned whether the bony segments of the dinosaur tails could have produced a supersonice boom. Even if that was possible, he said, using the tail like a whip might have been both painful and damaging to dinosaurs. The last few segments might even snap off.

In their report, Dr. Myhrvold and Dr. Currie emphasized that only the last two or three inches of the dinosaur tail would have exceeded the speed of sound. The possibility of pain or damage might be minimized or eliminated, they pointed out, if the most extreme part of the tail extended past the last vertebra as a piece of skin, tendon or keratin, the protein that can take the form of scales, claws or feathers. ''If whips made from the skins of cows and kangaroos are able to withstand supersonic motion,'' they said, ''why not dinosaur skin and tendons?''

But the two researchers agreed with the paleontologists who now reject the idea that the sauropods regularly used their tails defensively. The animals would probably have sustained as much injury to their tails as they inflicted on attackers.

As chief technology officer at Microsoft, Dr. Myhrvold presumably has more pressing research matters than dinosaur tails. But dinosaurs have fascinated him since childhood, and he has probably never met a research problem he did not try to use a computer to solve. He got in the habit of stretching the imagination when he studied cosmology under Dr. Stephen W. Hawking at Cambridge University in England.

''I don't claim it's relevant to Microsoft,'' he said of the dinosaur simulations. ''It's just an interesting problem to me.''